Functional MRI has been applied to the study of developmental change for over a decade. A growing number of fMRI studies have examined age-related changes in language organization. However, existing studies have predominantly targeted the detection of differences between children and adults in crosssectional designs and are limited as they only capture development at a single point in time, and thus the mechanisms by which these cognitive changes occur over time is still quite uncertain. Also absent from many existing studies are the theories explaining why language organization should be expected to change in childhood and how that change occurs. A better understanding of the mechanisms of cognitive change might broaden our understanding of cognitive development, elucidate the causes of atypical development, and could potentially inform our diagnosis, treatment, and prevention of developmental disorders. The current proposal is founded on a comprehensive theory of language development, which predicts organization from predominantly sensorimotor-based (bottom-up) processing in early stages to more strongly top-down controlled processing in later childhood and adulthood. Applied to two language tasks that tap into the two primary components of language development (lexicosemantic and morphosyntactic), this theoretical perspective generates specific hypotheses about developmental change that will be examined both in cross-sectional and longitudinal analyses. Theories of both constructive and regressive neural mechanisms of change inform the hypotheses that brain regions will have age-related differential involvement in language networks. These aims will be achieved using the noninvasive techniques of structural magnetic resonance imaging (MRI), functional MRI, and functional connectivity MRI (fcMRI) to map structural and functional brain networks. During functional imaging, subjects will complete a panel of language tasks: lexical semantic decision (assessing accuracy of sentences describing objects) and morphosyntactic judgment (assessing grammaticality of sentences). Participants will be age seven or nine for the initial imaging study, and will be scanned once more at twelve month intervals, providing a longitudinal component to the study. In addition, standardized cognitive measures will be administered outside the scanner to provide additional data for correlation with imaging data, allowing individual differences in development and ability to be taken into account.